DESCRIPTION (provided by investigator): There is uncertainty about the effect of low-level methylmercury (MeHg) exposure on neurodevelopment. Two seminal studies conducted in the Faroe Islands and the Seychelles Islands of prenatal MeHg exposure report inconsistent conclusions with respect to cognitive and behavioral outcomes. The primary aims of the proposed research are to investigate: 1) the association between prenatal MeHg and attention-associated behaviors among infants using the Neonatal Behavioral Assessment Scale (NBAS);and 2) the association between MeHg and behaviors associated with Attention Deficit Hyperactivity Disorder (ADHD) among school-aged children (median=8 years) using the Conners'Rating Scale for Teachers (CRS-T), the Neurobehavioral Evaluation System 2 (NES2) Continuous Performance Test (CPT), and components of the Wechsler Intelligence Scale for Children-Third Edition (WISC-III). We will also investigate a potential synergistic effect of MeHg and polychlorinated biphenyls (PCBs) on behavior and evaluate gender differences for the MeHg and behavior associations. Finally, we will assess the potential confounding effect of fish consumption on the association between MeHg and behavior. The study will be conducted among a birth cohort of 788 infants born between 1993 and 1998 to mothers residing adjacent to a PCB-contaminated harbor and Superfund site in New Bedford, Massachusetts. MeHg was measured in maternal hair collected at approximately 10 days postpartum. Associations with behavioral outcomes will be estimated with multivariable regression, controlling for a wide range of covariates. Results of this study will build upon the literature on the neurodevelopmental effects of MeHg. This is critical to arriving at consensus in informing the public about the potential hazard of prenatal MeHg exposure, given that the primary source of exposure is fish consumption, which is associated with substantial health benefits, including benefits to neurodevelopment. PROJECT HEALTH RELEVANCE The association between prenatal methylmercury (MeHg) and neurodevelopment is not well understood. This study will be an important contribution to the literature necessary for informing the public about the potential hazard associated with prenatal MeHg exposure, given the apparent benefit of fish consumption on the developing brain.